What's horrifying is that OE is actually quite good. But it's chock full of evil scripting security holes and requires care and attention to keep patched up to date.
However, the mail client in Mozilla/Netscape 6 is also very nice, and hooks up to LDAP servers nicely. And does IMAP.
Peter Shill For Hire [link|http://www.kuro5hin.org|There is no K5 Cabal]
It also has the very nice feature of running under Windows and Linux. So you can migrate them to Mozilla on Windows and if (when) you change to Linux (or Mac?) you get to keep the interface and all your old mail and address books.